docs: def validate(self, corpus):
          """
          Perform the validation on the given corpus.
  
          Args:
              corpus (Corpus): The corpus to test/validate.
  
          Returns:
              InvalidUtterancesResult: Validation result.
          """
          invalid_utterances = {}
  
          for utterance in corpus.utterances.values():
              if self.label_list_idx in utterance.label_lists.keys():
                  ll = utterance.label_lists[self.label_list_idx]
  
                  if len(ll) < self.min_number_of_labels:
                      invalid_utterances[utterance.idx] = 'Only {} labels'.format(len(ll))
              else:
                  invalid_utterances[utterance.idx] = 'No label-list {}'.format(self.label_list_idx)
  
          passed = len(invalid_utterances) <= 0
          info = {
              'Min. number of labels': str(self.min_number_of_labels),
              'Label-List ID': self.label_list_idx
          }
  
          return base.InvalidUtterancesResult(passed, invalid_utterances, name=self.name(), info=info)